The present invention relates to a method of producing a semiconductor device using an SOQ (Silicon On Quartz) substrate in which a semiconductor layer is formed on a quartz substrate, and to the SOQ substrate used in the method. More specifically, the present invention relates to a method of producing a semiconductor device applicable to a transmission projector and an SOQ substrate used in the method.
A conventional SOQ substrate is formed of a quartz substrate (an insulating substrate) and a silicon layer formed on the quartz substrate. A completely depleted transistor formed of the conventional SOQ substrate provides a low S value and a low substrate floating effect. Further, the completely depleted transistor provides advantages such as a low connection capacity, a high operation speed, low power consumption, and excellent radiation resistance.
Patent Reference has disclosed a structure in which a conventional SOQ substrate is formed of a quartz substrate and a silicon layer formed on the quartz substrate. Patent Reference has also disclosed a TFT (Thin Film Transistor) formed on the conventional SOQ substrate.    Patent Reference: Japanese Patent Publication No. 2008-147227
In general, quartz has hardness lower than that of silicon, and a smaller thermal expansion coefficient as compared with silicon. Accordingly, quartz tends to expand or contract more easily due to a difference in the thermal expansion coefficient. Especially when a film with high tension stress is formed on a quartz substrate, the quartz substrate is difficult to withstand the tension stress, thereby causing a crack in a contact region on the quartz substrate.
Such a crack tends to occur in a shallow and fine region, so that it is difficult to detect the crack with naked eyes or visual inspection. In order to secure device quality management and reliability, it is imperative to accurately detect a crack. Accordingly, it has been required as a technical issue to establish a reliable method of detecting a crack.
In the past, an entire portion of a wafer is inspected to detect a crack on a device. As explained above, however, it is difficult to detect a crack, thereby increasing time and cost for inspecting a large number of wafers.
In view of the problems described above, an object of the present invention is to provide a method of producing a semiconductor device capable of solving the problems of the conventional technology. In the invention, it is possible to easily detect a crack on an SOQ substrate. Another object of the present invention is to provide an SOQ substrate capable of easily detecting a crack.
Further objects and advantages of the invention will be apparent from the following description of the invention.